Approaches for automated management of virtual machines for running untrusted code safely

ABSTRACT

Approaches for transferring data to a client by safely receiving the data in or more virtual machines. In response to the client determining that digital content, originating from an external source, is to be received or processed by the client, the client identifies, without human intervention, one or more virtual machines, executing or to be executed on the client, into which the digital content is to be stored. In doing so, the client may consult policy data to determine a placement policy, a containment policy, and a persistence policy for any virtual machine to receive the digital content. In this way, digital content, such as executable code or interpreted data, of unknown trustworthiness may be safely received by the client without the possibility of any malicious code therein from affecting any undesirable consequence upon the client.

CLAIM OF PRIORITY

This application claims priority to U.S. non-provisional patentapplication Ser No. 13/115,354, filed May 25, 2011, entitled “Approachesfor Securing an Internet Endpoint using Fine-Grained Operating SystemVirtualization,” the contents of which are hereby incorporated byreference for all purposes as if fully set forth herein, having apriority date of May 28, 2010.

FIELD OF THE INVENTION

Embodiments of the invention relate to the automated management ofvirtual machines.

BACKGROUND

Ensuring the security of Internet users and Internet connected devicesis one of the grand challenges facing us today. The current state ofaffairs is very problematic, as our cyber-security infrastructure iseasily and routinely subverted by cyber criminals, resulting in greateconomic loss. Every year brings deeper and more complex dependence bysociety on our cyber-infrastructure, and yet at the same time thecyber-security problem only worsens as the capabilities of thecyber-criminal mature. In effect, we are building mission-criticaldependence into virtually every aspect of human activities on acyber-infrastructure that is very insecure at its core.

The current state of our cyber-security infrastructure is due to twofundamental limitations. The first limitation is a fundamental mismatchbetween the design assumptions made by computer security programmerswith how the vast majority of users interact with thecyber-infrastructure (the “Security Model Complexity” problem. Thesecond limitation is a lack of appropriate isolation of code and datafrom trusted and untrusted sources in modern computer systems (the “Lackof Isolation” problem). These two limitations of current systems aresomewhat orthogonal, but are both very important for securing anendpoint. The “Lack of Isolation” problem, in particular is veryimportant because modern computer systems that are used for everydaycomputing as endpoints are typically general purpose devices capable ofrunning a vast variety of software from different sources.

The general purpose capability of modern endpoint systems is constructedusing a layered stack of hardware and software. An example of thelayered arrangement of hardware and software that is present in moderncomputer systems is shown in FIG. 1. At the lowest layer, there ishardware with a small number of basic general purpose programmingcapabilities. Upon this hardware layer sits the firmware and operatingsystem (OS) layers. The firmware and OS layers provide higher-level butbroad capabilities such as managing specific devices, files, and/orprocesses. On top of the OS layer run the various applications whichprovide user-visible rich functionality to the computer. Thefunctionality provided by the application layer is typically the primaryconcern of the computer user.

One advantage and consequence of the layered nature of modern computersystems is that the various layers may come from different vendors, aslong as the layers conform to the specifications governing the layerboundary (which may be based on open or proprietary industry standards).To illustrate an example, in a typical PC today the hardware may beconstructed around processor and chipset technology provided by Intel orAMD. The firmware/BIOS may be provided by companies like Insyde, AMI orPhoenix and may be written to conform to several industry specificationssuch as UEFI and PI. The operating system (OS) may originate from acompany like Microsoft or Apple or may be a flavor of the Linux opensource OS. Finally, the applications themselves are usually written tothe specification of one of the operating systems and may be provided byone of a large multitude of application vendors.

Note that some of the applications may themselves have a layeredarchitecture. A web browser, for example, typically includes a browsercore and may also download web applications in the form of HTML,Javascript and Flash programs from various Internet web sites. The webbrowser may run these downloaded web applications locally on top of thebrowser core. A typical web page contains HTML with embedded JavaScriptthat can change the HTML being rendered by the web browser dynamicallybased on user actions without having to re-download the web page fromthe web server. The HTML may also demarcate part of the web page to berendered by a plugin, which is typically a separate program that isinstalled on the computer. Plugins are also often downloaded fromdifferent sources over the World Wide Web. Thus, a modern computer runscode that comes from a variety of different sources. In particular,application programs may originate from literally millions of differentsources once we consider the collection of traditional localapplications as well as web applications that are downloaded fromwebsites.

The integrity of a computer system when it runs application code fromdifferent sources (or even the same program being run by different usersof a shared computer) has traditionally been one of the responsibilitiesof the OS. The OS uses various hardware and software constructs likevirtual memory, processes, and file permissions to prevent code and databelonging to one program (or user) from affecting code and databelonging to another program (or user). This responsibility of the OS to“isolate” programs and data from one another often tends to compete withanother responsibility of the OS, which is to allow for co-operationbetween programs especially between user application programs and systemlevel services such as shared library modules, database services, andother higher-level common OS functionality. These two OS functions, toshare and to isolate, require the OS designer to make some tradeoffs onhow much to share and how much to isolate.

As a result of these tradeoffs, the resulting implementation of modernoperating systems tends to be overly complex and typically exhibitnumerous bugs. In mature operating systems, the security implementationis typically robust enough to work well for normal programs under normalusage with no adverse impact on the operation of the computer. However,most OS implementations are very large and complex bodies of computercode. For example, an OS implementation may have thousands of loopholesthat cause a security system to break down under situations whereprograms are especially constructed to take advantage of less-tested orunvalidated corner cases in the operation of the security subsystem.Furthermore, the security implementation of modern operating systemsdoes not perform well when all programs are initiated by the same user.

These “security vulnerabilities” are not important for well behavedprograms during typical operation, but are used extensively by cybercriminals to subvert the computer's security subsystems. Once thesystem's security is subverted, it is generally possible for cybercriminals to run any software under their control on the subvertedcomputer system.

The Lack of Isolation problem is made worse by the fact that a largeamount of code executed by computers today comes from sources outsidethe computer, some of which have explicit intentions of committingcriminal activities. This includes any program downloaded from theInternet or any web site visited by the computer. All downloadedprograms (good and bad) have the same OS and library services availableto them to use during their operation. Consequently, any program (evenmalware), can exploit any security vulnerability in the complex OS orweb browser environment and subvert the security subsystem that isolatesapplications from one other. For example, when a user visits a web site,he or she is really running web application code developed by thepublisher of the web site. If this web site is malicious, then malwaremay be executed on the computer. Malware may be designed to exploit asecurity vulnerability in the web browser to take control of thecomputer system during subsequent web site visits, e.g., if you visityour bank's web site, your key strokes may be captured and yourlogin/password information for the bank may be transmitted to themalware publisher.

Most computer security professionals understand the existence of theLack of Isolation problem, but consider it hard to solve in anypractical way because better achieving the goal of isolation betweenapplications fundamentally tends to conflict with achieving the goal ofincreasing seamless communication between different local and webapplications. There has been some work towards the isolation of web codefrom different sources being run by a web browser. Modern browsers haveattempted to create a level of sandboxing around downloaded webapplication code in order to isolate downloaded code from the rest ofthe computer and from each other. However, these models are fairlyprimitive in their ability to deal with the full gamut of securityissues that arise during the course of a typical user's web experience.For example, certain versions of Google's Chrome web browser'ssandboxing does not address safety issues arising from downloadedbrowser plugins and various types of native executables; thus, everycomputer system running certain versions of Chrome is vulnerable to azero day exploit attack against Adobe Flash or Microsoft Word as much asif the system was running a less secure or older browser with the sameAdobe Flash Plugin or Microsoft Word plugin.

Web browsers have been burdened with the need to ensure fullcompatibility to older and non-standard web pages in their efforts toprovide superior safety and privacy. For example, web browserprogrammers have had to make some relaxations around the same-originpolicy in order to correctly render popular web sites that rely on thesharing of information between web sites.

Last but not least, most web browsers vendors suffer from a hugeconflict of interest because their business relies upon monetizing theweb browsing habits of their users within their own business processesand with their industry partners. This monetization relies on data aboutusers' browsing habits which is contained in the web cookies that areset and later provided to web servers during the course of web sessions.Companies such as Google and Microsoft have a great interest in learningas much as possible about a person's browsing habits and typicallyarrange the default privacy settings of web browsers to be advantageousto them (but less than optimal from a security and privacy standpoint).This choice of default privacy and core functionality settings causesweb browsers to transfer large amounts of sensitive information from endusers' machines to Internet related businesses, such as Google,Microsoft, Apple, etc., thereby allowing such businesses to bettermonetize their customer base by offering appropriate products andservices and serving targeted ads. These same settings, however, can beleveraged by malicious parties to exploit security vulnerabilities.While all web browsers provide some level of control to thesophisticated user to tune his or her web browser functionality and/orprivacy/safety settings to browse more securely, the vast majority ofusers never change these default settings.

Some security researchers have also proposed the use of “clientvirtualization” (also called “Virtualization using a Hypervisor” in thedesktop) to solve the Lack of Isolation Problem. In one form of clientvirtualization, the user runs multiple independent operating systems ontheir laptop or desktop on multiple virtual machines (VMs) within theclient system which have been created using a hypervisor, such as fromVMWare of Palo Alto, California or Virtual PC, available from MicrosoftCorporation of Redmond, Washington. When client virtualization is usedto achieve improved security, different VMs are used to run applicationsfrom different sources or of different types. For example, an OS in oneVM may be dedicated for accessing the corporate network that the usermay be part of and running corporate applications (local and web).Another OS in a second VM might be used by the user to run his or herpersonal programs and store personal documents. Finally, a different OSin a third VM may be used for general web browsing on the wider Internetand running native executables that may have been downloaded from theInternet. An example of such a solution is XenClient, which is made byCitrix Systems of Ft Lauderdale, Fla.

The use of classical client virtualization, as discussed above, to solvethe general code isolation problem in the context of Internet endpointssuffers from several drawbacks. A first drawback is that there is toomuch management overhead for the end-user. The end-user has the onus ofmaking the decision as to what VM to use for each activity. Any mistake,intentional or accidental, may subvert the integrity of the system.While many safeguards can be added as a layer on top of the corevirtualization technology to prevent the user from making mistakes, thishas not yet been demonstrated to work in a practical and robust fashion.

Another drawback is that this arrangement of VMs is very static and doesnot lend itself to the dynamic and varied nature of the typical user'sactivities. For example, depending on the time of the day, many usersmay need to isolate programs from 2 sources to 10s of sources. In thearrangement described above, there is no VM based isolation between allthe web sessions of the user on the general Internet. Running 10s of VMson a single client system all the time leads to too much performance andmanagement overhead using prior approaches. Starting VMs on demand forindividual activities suffers from huge latencies to start activitiesand a limitation on the number of concurrent activities supported, whichadversely affects the user experience.

An additional drawback is that client virtualization, as describedabove, suffers from the problem that any VM that is used for general webbrowsing is just as vulnerable to a security problem as any monolithicsystem running a single VM while accessing web sites on the generalInternet. Therefore, it is quite likely that the VM dedicated to webbrowsing described in the arrangement above will be subverted by malwareeventually. Any subsequent activities in that VM, then, will becompromised.

Due to these reasons client virtualization has not been used widely toimprove the security of Internet endpoints.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are illustrated by way of example, and notby way of limitation, in the figures of the accompanying drawings and inwhich like reference numerals refer to similar elements and in which:

FIG. 1 is an illustration of the layered arrangement of hardware andsoftware present in modern computer systems;

FIG. 2 is an block diagram of the functional components of oneembodiment of the invention;

FIG. 3 is block diagram of the functional components involved inexposing a restricted copy of the file system to different UCVMs (andVVMs) according to an embodiment of the invention;

FIG. 4 is a flowchart illustrating the steps involved in a UCVMobtaining a copy of a new user file maintained in the file system storedelsewhere according to an embodiment of the invention;

FIG. 5 is an illustration of instantiating a plurality of differentvirtual machines using different templates according to an embodiment ofthe invention;

FIG. 6 is an illustration of a virtual disk based on VSS shadow copiesaccording to an embodiment of the invention;

FIG. 7 is an illustration of exemplary desktop of a client according toan embodiment of the invention;

FIG. 8 is an illustration of safely installing an untrusted applicationaccording to an embodiment of the invention of the invention; and

FIG. 9 is a block diagram that illustrates a computer system upon whichan embodiment of the invention may be implemented.

DETAILED DESCRIPTION OF THE INVENTION

Approaches for the automated management of virtual machines arepresented herein. In the following description, for the purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the embodiments of the invention describedherein. It will be apparent, however, that the embodiments of theinvention described herein may be practiced without these specificdetails. In other instances, well-known structures and devices are shownin block diagram form or discussed at a high level in order to avoidunnecessarily obscuring teachings of embodiments of the invention.

Functional Overview

Embodiments of the invention prevent malicious code, introduced into acomputer system, from compromising the resources of the computer systemthrough the use of dynamic operating system (OS) micro-virtualization. Acomputer system of an embodiment includes a number of independentvirtual machines (VMs) that each executes a full operating system (OS).A block diagram of client 200 according to one embodiment of theinvention is shown in FIG. 2. The term “client,” as broadly used herein,represents any type of Internet endpoint or computer system capable ofconnecting to a network and executing a virtual machine. Non-limiting,illustrative examples of client 200 include a PC, a laptop computer, atablet computer, a cell phone, a personal digital assistant (PDA), andthe like.

In an embodiment, client 200 may correspond to a server. Thus, while useof the term “client” in other contexts might exclude an interpretationthat includes a server, as broadly used herein, client 200 may beembodied on a wide variety of machines, one example of such being aserver. Thus, as the Applicant may be his or her own lexicographer, asused herein, the term client 200 expressly includes a server. Forexample, non-limiting, illustrative examples of client 200 include a webserver, an application server, a file server, and a cloud server.Indeed, implementing embodiments of the invention upon a server mayyield many benefits. The micro-virtualization techniques employed byembodiments provide an efficient mechanism for eliminating the risk ofexecuting untrusted code and/or interpreting untrusted data inaccordance with different policies to manage such risk. As such, adevice, such as a server, which interacts with (a) numerous sources ofuntrusted code and/or data and/or (b) two or more corporate entitieshaving different policies towards managing the risk of untrusted codeand/or data, may benefit from embodiments of the invention.

Client 200 includes a number of virtual machines (such as 230, 240, 250,and 260, for example) that execute on hardware 210 of client 200. Thevarious VMs within client 200 may be used for separately executingprocesses associated with different activities. One such VM, namely“VMO” (i.e., VMO 230 of FIG. 2), is secured so that VMO may serve as theroot of trust with a guaranteed integrity. VMO may contain coreoperating system 232 and one or more applications 234. In the embodimentshown in FIG. 2, VMO is not accessible over any network, such as theInternet. As shall be explained below, VMO provides a secure environmentin which operating system 232 and one or more applications 234 mayexecute without risk of exposure to malicious code.

Other VMs, such as VMs 260, 262, 264, and 266 in FIG. 2, may be created,maintained, and destroyed on-demand using a very efficientmicro-virtualizing hypervisor 220. Using efficient micro-virtualizationtechniques, the latency of starting and stopping activities orapplications which run in their own VM in embodiments is very low,thereby providing a practical user experience while employing full OSvirtualization.

Embodiments address and overcome many disadvantages, such as the Lack ofIsolation Problem, experienced by modern general purpose computersystems that execute code from different sources and of differing trustlevels; nevertheless, embodiments maintain compatibility with currenttypical real-world usage of computer systems by corporate andnon-corporate users. This is so because any activity which is notpreviously deemed trustworthy is performed in a separate VM by certainembodiments, and so all code which may be potentially malicious isexecuted in its own VM that is destroyed after its immediate use isended, thereby preventing any malicious code from effecting any lastingchange to a computer system according to an embodiment of the invention.

The Trusted Vitual Machine—VMO

In an embodiment of the invention, a special virtual machine, referredto herein as “VMO,” is created to be a trusted and un-hackable portionof a computer system. FIG. 2 depicts VMO 230 according to an embodiment.To achieve the property of being un-hackable, VMO 230 may be permanentlydisconnected from any network (i.e., VMO 230 is not connected to anylocal network or the Internet). Specifically, VMO 230 may not containany type of networking stack, such as a TCP/IP network stack, and maynot have access to any networking hardware that could allow forcommunication between VMO 230 or any applications 234 executed therebyand the Internet. Thus, the only way to install software onto VMO 230 isto have physical custody of client 200 and manually install the softwareon VMO 230.

Thus, in certain embodiments, one or more applications 234 executingwithin VMO 230 do not have any access to a network, must be fully selfcontained in their functionality, and must rely only on local code anddata for all their functionality. All applications that need to accessthe network will therefore need to run in a separate virtual machineoutside of VMO 230, as shall be described in further detail below. It isenvisioned that the software (such as one or more applications 234)running in VMO 230 be selected at the time client 200 is manufactured orfirst configured for use in a controlled environment. Because VMO 230 isnever connected to any type of network, such as a TCP/IP network, allcommon types of network initiated attacks cannot be waged against VMO230, thereby rendering VMO 230 immune to such attacks and safe ascompared to any computer or VM that is connected to the Internet.

In an embodiment where hypervisor 220 is a Type 2 hypervisor, whenclient 200 is booted, only VMO 230 is started by the BIOS or firmware ofclient 200. Once VMO 230 is running, VMO 230 can start hypervisor 220immediately or on demand. In another embodiment, where hypervisor 220 isa type 1 hypervisor, hypervisor 220 is first started by the BIOS whenclient 200 is booted and VMO 230 is launched by the Hypervisor 220.Hypervisor 220 is a software component that is responsible for creatingother VMs which each execute independent instances of the operatingsystem. These additional VMs are instantiated by VMO 230 and/orhypervisor 220 to run any untrusted code or code that needs to accessthe network. Untrusted code in this context is any code which has notbeen pre-approved as being trusted by an IT administrator of client 200.The additional VMs are started “silently” and automatically by client200, e.g., these VMs are started transparently to the user and withoutthe user having to do anything explicit. These additional VMs are alsonot explicitly visible to the user; instead, all the user sees on thedesktop is familiar objects (such as icons, windows, and applications)without any indication that multiple VMs are executing in client 200.Embodiments of the invention follow rules that govern what applicationactivities are assigned to which particular VM. These rules aredescribed below in greater detail.

In another embodiment (not depicted in FIG. 2), VMO 230 may have anetworking stack that is firewalled off from the network usingwell-tested firewall software, thereby allowing VMO 230 to have accessto a computer network. Such an embodiment may only allow connectionswith a specific Internet system so that the software inside VMO 230 maybe updated from a designated update server. For example, the firewallsoftware may only allow VMO 230 to connect to one or more serversassociated with the IT administrator of client 200 and may prevent VMO230 from establishing a connection with any other endpoint on anynetwork.

Interaction with an User Interface

All code responsible for generating a user interface (UI) not associatedwith an application may be maintained in VMO 230. Consequently, all UIinteraction activity with the desktop between a user and softwareexecuting on client 200 may take place between the user and VMO 230,which maintains a unified desktop for all applications running in allVMs. Interaction between the user and applications running in VMs otherthan VMO 230 takes place indirectly via VMO 230. For example, when theuser enters a password for a web site whose browser and HTML/Javascriptcode is running in an untrusted VM, the password is first directlyprovided to VMO 230, which then transfers the information to theuntrusted VM. Furthermore, the untrusted VM's display is rendered on toa virtualized display, which is then composed into the VMO 230 desktop(as appropriate) by controlling code running in VMO 230. As codeexecuting in VMO 230 is trusted, the user may trust any user interfacecontrols displayed on a screen since all code responsible for renderingthe user interface is trusted.

This approach is quite different from prior systems where often the codethat controls the full desktop experience is untrusted. Consequently, ifthe code responsible for generating the user interface is corrupted bymalware, then the user interface may be used as a tool to deceive theuser. For example, malware may cause a user interface control to bedisplayed that requests the user to submit an authentication credentialwhich will be used for improper purposes by the malware. However, thisproblem is overcome by embodiments of the invention—since all coderesponsible for rendering user interface controls executes in VMO in anembodiment, malware is prevented from hijacking or corruptingUI-rendering code.

To illustrate an embodiment of the invention, consider FIG. 7, which isan illustration of exemplary desktop of client 200 according to anembodiment. As shown in FIG. 7, process 704 is responsible for renderingdesktop 706 on a physical display of client 200. Process 714A runs inuntrusted VM 714 and does not have complete access to the file system ofclient 200. When any process inside VM 714 requests access to the filesystem of client 200, it is intercepted and process 702 is responsiblefor rendering a window 708 depicting the contents of the file system ofclient 200. Process 702 has the option of selectively displaying whichcontents are available to the VM 714 based on policies as set forth bythe IT administrator or the user. VM 710 in FIG. 7 that runs thesolitaire game is implemented such that the display of VM 710 is avirtualized display, which is then composed into the desktop 706 (asappropriate) by controlling process 704 running in VMO 230. The displaysof VMs 712 and 714 are rendered on the desktop 706 in a similar fashion.

The Legacy Virtual Machine—LVM

FIG. 2 depicts a legacy virtual machine (LVM) 240 according to anembodiment of the invention. LVM 240 may contain operating system 244.LVM 240 serves as the primary entity being managed by the ITadministrator of client 200. As such, LVM 240 provides an environmentthat is analogous to the managed enterprise OS of corporate computersystem in that an IT department may install and maintain variousenterprise applications within operating system 244 of LVM 240. In anembodiment, operating system 244 of LVM 240 may correspond to aMicrosoft Windows OS or any other general purpose OS such as Linux orMacOS.

In an embodiment, LVM 240 is responsible for storing the main filesystem 242 of client 200. File system 242 may contain the user's profilefolder containing the user's settings and files.

LVM 240 typically only runs infrastructure OS programs and programs thatare used for the purpose of managing client 200 and trusted enterpriseapplications. Other user programs (especially those that involveexternal components or consume untrusted data) do not run in LVM 240,but instead, run elsewhere in separate VMs (such as a UCVM as describedin more detail below).

In an embodiment, the network access of LVM 240 is restricted to justthe corporate network as implemented by firewall VM 250. Firewall VM 250is a specialized virtual machine that comprises firewallsoftware/applications to restrict network access of VMs running inclient 200 to appropriate and/or necessary network access points. Suchpractice is consistent with the need for only the responsible ITadministrator to be capable of connecting to LVM 240 to manage LVM 240and processes executing therein.

In one embodiment, LVM 240 and VMO 230 may be implemented in a singlevirtual machine.

Untrusted Code Virtual Machine—UCVM

When a user wishes to run any application that requires access to eithera network or untrusted data (untrusted data is any data that originatesfrom outside client 200), the application is run inside a dedicated VMthat is created on-demand by hypervisor 220. This dedicated VM is calledan Untrusted Code Virtual Machine (or UCVM). FIG. 2 depicts severalUCVMs, namely UCVM 260, 262, 264, and 266. A UCVM operates under theassumption that, in general, any code that connects to the network andinteracts with arbitrary code executing on an external device may atsome point be compromised. This assumption also applies to trustedapplications that interact with data originating from outside thecomputer system executing the trusted application, because such datamay, at some point, contain embedded malicious code. To address suchpossibilities, such applications are executed in a UCVM to prevent anymalicious code, inadvertently introduced into the UCVM, from having thecapacity to affect any change outside of the UCVM.

In an embodiment, a UCVM is created by (a) cloning a copy of LVM 240, ora stripped-down version of LVM 240, in memory and (b) providing accessto a restricted file system to the newly created UCVM. For example, UCVM260 comprises restricted file system 260A, UCVM 262 comprises restrictedfile system 262A, and UCVM 264 comprises restricted file system 264A.Each UCVM possesses its own instance or copy of the operating system,which is isolated and separate from the main operating system (includingits code and data) executing within VMO 230 or LVM 240. For example,UCVM 260 comprises operating system 260B, UCVM 262 comprises operatingsystem 262B, and UCVM 264 comprises operating system 264B.

To provide a low latency user experience, UCVMs may not be booted fromscratch each time an application is needed to be started. Instead, aUCVM may be created very quickly by cloning the UCVM from a template VM(with a booted OS) that has been pre-loaded in memory at system boottime. In an embodiment, the template used to clone a UCVM may beselected from templates 238 stored in VMO 230. A variety of techniquescan be employed to make this cloning operation as fast as a few 100milliseconds. Multiple types of templates may be used by a system tocreate UCVMs depending the nature and type of application(s) to be runinside the UCVM, as discussed in greater detail below in the sectionentitled “Cloning a UCVM from a Template.”

Cognitive assist module 236 is software that is responsible forimplementing the rules and policies of embodiments as well as helpingthe user of client 200 in understanding and navigating the securitymodel employed by client 200 on an as-needed basis. Cognitive assistmodule 236 helps decide what activities run in which UCVMs, includingwhen VMs are created or destroyed, and what kind of access to networkand file system resources each UCVM has. Cognitive assist module 236also helps protect the user, e.g., when a user is fooled by malwarerunning in a UCVM and is in the process of providing some informationthat they have previously provided to enterprise code running in LVM 240(for example a password), then cognitive assist module 236 may detectthis situation and prevent the user from providing the information(which may be secret corporate information) to the malware.

Regarding the restricted file system of each UCVM, each UCVM has accessto a private copy of a subset of the files in file system 242 on client200. A UCVM may only have access to those files which the UCVM shouldneed for the correct operation of the application executing therein. Forexample, user files are usually not required for correct operation of anapplication executing in a UCVM and thus are not typically exposed to aUCVM. On the other hand, if a UCVM is created as a result of the userwishing to edit a document using an application, such as MS Word, then acopy of the document the user wishes to edit will be provided to therestricted file system of the UCVM at the time the UCVM is created.Advantageously, using UCVM 260 as an example, if a process executingwithin UCVM 260 makes any changes to any files in restricted file system260A, then these changes do not impact the files stored in file system242 maintained in LVM 240 because such changes are only made torestricted file system 260A maintained in the UCVM and are notpropagated, without express consent from the user, to file system 242maintained by LVM 240.

In a typical use case of a UCVM, the UCVM may run a local application oran individual web page session. When a user is done running the localapplication or navigates away from a web page to another page with adifferent Internet URL domain, the corresponding UCVM is destroyed. Anynew local application or web application will be run inside a brand new,separate UCVM that is cloned again from a clean UCVM master template.Thus, if there has been any compromise to the UCVM during the course ofrunning some malicious code that was introduced into the UCVM, then theadverse affects of the security breach are isolated to only the affectedUCVM and are lost when the UCVM is destroyed.

For example, assume that a user double-clicks on a MS Word document iconin Windows Explorer. Embodiments create a special UCVM to run the MSWord process. In a particular embodiment, cognitive assist module 236 ofVMO 230 may dynamically create the UCVM using a template in one or moretemplates 238 or use a pre-existing template in memory or on the disk.The template selected by cognitive assist module 236 may be selectedbased on what activity is to occur within the UCVM, i.e., the selectedmay be designed to create a UCVM having characteristics that are optimalfor running a text editor therein. The created UCVM contains a copy ofthe operating system as well as a restricted (local) copy of the filesystem. This local copy of the file system in the UCVM contains all theusual Windows and Program files; however, the user's profile folder inthe local copy of the file system contains only the single target MSWord document being opened.

As another example, assume that three tabs are open in a web browser andfurther assume that each tab is open at a different web page. Inconsideration of the code which may be contained or embedded on a webpage, each web page may be properly considered a web application. Inembodiments of the invention, the code responsible for rendering theuser interface (UI) of the web browser runs in VMO 230. On the otherhand, executable code for the three web applications runs in threeseparate UCVMs. A core HTML/Javascript engine runs in each of the threeUCVMs. A copy of the file system within each of the three separate UCVMsdoes not contain any part of the user's files, as they are not requiredfor the task performed by each UCVM, namely displaying a web page. Thus,each web application (or web page in this example) is completelyisolated from the rest of the system.

In an embodiment, a UCVM may be connected to the Internet according toan access policy determined by the nature of the code running within theUCVM. To illustrate, web pages are typically restricted as per a strict“same origin policy” similar to the rules implemented by modern webbrowsers. In the “same origin policy,” scripts running on web pages arepermitted to access methods and properties of other scripts originatingfrom the same site with no specific restrictions, but are prevented fromaccessing most methods and properties across web pages on differentsites. Untrusted native applications running outside of the web browserare restricted by default to be able to connect only to the domain fromwhich the program was downloaded (and to specific content deliverynetworks (CDNs) that may be in use by the domain in question).

This level of network access for downloaded applications can beexplicitly changed (increased or decreased) by the end-user to includeadditional sites on the Internet. End-user control over what a UCVM canconnect to may be subject to certain limitations related to corporatenetworks and sensitive web sites (such as a bank and web mail provider).For example, any code running in a UCVM may not, in general, access anysite on a corporate Intranet to which client 200 is connected.Applications that need to connect to the corporate Intranet may need tobe signed by the IT administrator of the domain. Similarly, non-webuntrusted application code in a general UCVM may not connect to a website associated with a search engine or bank or other sites that mayhave been previously identified as being “off limits.” These connectionscan only be made through a web browser (which spawns UCVMs bound tothese special domains) or from a special purpose LVM called a VVM, whichdescribed in further detail below.

In an embodiment, there is no communication channel available for anapplication running in one UCVM to communicate with an applicationrunning in another UCVM. Thus, applications running in UCVMs arecompletely isolated from each other and from the other applications inthe system. This is well suited for running downloaded third party localapplications which are generally designed to be self-contained or forInternet applications (web pages are not supposed to rely on anycommunication between applications within the web browser). In analternate embodiment, communication between an identified set of virtualmachines can be enabled by a person with sufficient privileges, such asan IT administrator for client 200.

Firewall Virtual Machine

In an embodiment, the implementation of the network access restrictionsis done in a dedicated VM called a firewall VM. FIG. 2 depicts anexemplary firewall VM 250 of an embodiment. Firewall VM 250 runs anisolated operating system with a dedicated and fixed set of firewallapplications that implement the network access policy for all VMs inclient 200 (except perhaps VMO 230, which may not have any networkaccess). Firewall VM 250 may provide, to any virtual machine running onclient 200 in which untrusted code is executed or untrusted data isbeing interpreted, restricted access to only those network resourcesdeemed necessary on an as-needed basis in accordance with a policydescribed by policy data stored on client 200.

In another embodiment of the invention, the firewall functionality ofthe system may be co-located and implemented inside either thehypervisor 220 of FIG. 2, or inside the LVM 240 of FIG. 2 (working inconjunction with the hypervisor 220 of FIG. 2), or inside VMO 230 ofFIG. 2 (working in conjunction with the hypervisor 220 of FIG. 2).

Validated Virtual Machines—VVMS

UCVMs are not appropriate to run local applications that interactheavily with each other using local APIs such as COM, as typically thereis no communication channel available for an application running in oneUCVM to communicate with an application running in another UCVM.Embodiments may employ one (or more) special UCVMs called a ValidatedVirtual Machine (VVM) for the purpose of running relatively trustedlocal applications that have complex interactions between theapplications. Such complex interactions are common in enterpriseframeworks containing multiple applications, such as Microsoft's OfficeSuite and IBM's Lotus Notes.

FIG. 2 depicts an exemplary VVM 266 of an embodiment. Note that whileFIG. 2 depicts a single VVM for ease of explanation, other embodimentsof the invention may employ two or more VVMs or no VVMs based upon theparticular needs of the user and/or policies of the organizationresponsible for or the owner of client 200.

Applications need to be signed and configured for co-location in thesame VM by an administrator of client 200 before they can run in VVM266. Inside VVM 266, signed applications can interact with each otherusing all types of APIs and frameworks supported by the OS being used.In an embodiment, the default network access policy of a VVM is to allowaccess to a corporate network only. The IT administrator may increase ordecrease this level of access, subject to certain restrictions.

In an embodiment, specific signed applications or suites (groups ofapplications) that originate from a trusted source (other than theenterprise) may also be designated to run together in a particular VVMresponsible for applications originating from that source. For example,all non-corporate applications that are signed by a specific vendor maybe run together in a single VVM. These applications would then beisolated from corporate applications and general untrusted applications,but not from one another. A specific network access rule that is morepermissive than the “same origin policy” used for web applications andunsigned applications may be used for a VVM. The restricted copy of filesystem 242 exposed to a VVM is similar to that exposed to a generic UCVMin that the restricted copy of file system 242 exposed to a VVMcomprises only those files related to, or required for, performance ofthe applications executing within the VVM.

The Restricted File System Exposed To A VM

FIG. 3 is block diagram of the functional components involved inexposing a restricted copy of file system 242 to different UCVMs (andVVMs) according to an embodiment of the invention. File System Switch310 is software that is configured to provide the newly created UCVMwith access to a copy-on-write clone of the OS image that the UCVM wascreated from once the UCVM has started. The minimal operating system andprogram files 330 in the copy-on-write clone may be created from eitherthe corporate LVM OS image 320 or a separate generic stripped down OSimage 322 which may be created by the IT administrator.

Furthermore, a newly created UCVM is provided a copy of necessary userfiles 340, which are a subset of the user files in file system 242. Thecomposition of necessary user files 340 will be different for each user.The set of files comprising the user files in file system 242 maintainedin LVM 240 are typically those files in the user's home folder, e.g.,c:\Users\<username>. The particular copies of files that are provided toa particular UCVM as necessary user files 340 are the minimum set offiles that are needed by that UCVM to accomplish what the user intendedto do as captured when the target application was being invoked. Forexample, if the user double clicked on a specific MS Word file namedABC.docx at the location c:\Users\<username>\Documents in the filesystem 240 maintained in LVM 240, then necessary user files 340 wouldonly include a copy-on-write clone of the ABC.docx file and only thiscopy-on-write clone of the ABC.docx file is made available in thevirtual c:\Users\<username>\Documents folder made visible to the newlycreated UCVM running the MS Word application. If a program (like MSWord) was started without any association with a file, then necessaryuser files 340 would correspond to an emptyc:\Users\<username>\Documents virtual folder.

Any application running in a UCVM therefore only has access to theparticular set of user files provided explicitly by the user when theprogram was invoked. Subsequently, if the user wants to browse filesystem 242 for another file from within the application (for example, byusing the File→Open menu item of MS Word), then he or she will see arestricted user files directory.

To enable the user to select files from the user's own User Files folderin file system 242 maintained in LVM 240 using an application executingwithin an UCVM, a user interface may be provided to allow the user tobrowse his or her files in file system 242, select one or more of theuser files, and expose a copy of the selected files to the appropriateUCVM. For example, FIG. 4 is a flowchart illustrating the steps involvedin a UCVM obtaining a copy of a new user file maintained in file system242 according to an embodiment of the invention. In step 410, a specialfile is provided to each UCVM. The special file may be provided to theUCVM in a number of different ways, e.g., the special file may beinserted into each folder of the virtual C:\Users\<username> directoryprovided to each UCVM. This special file may be named something akin to“Show All My Files” or the like, as its selection will be used totrigger exposing additional copy-on-write clones of files stored in filesystem 242 to the UCVM.

In step 420, File System Switch 310 detects when the special file isselected by the user. For example, when a program executing within aUCVM browses to the special file, presumably as a result of a userclick, this action may be trapped by File System Switch 310.

In step 430, File System Switch 310 invokes a dialog with LVM 240 thatallows the user to browse the full file system 242 maintained in LVM240. The user may then select a file or folder in file system 242. Notethat at this stage, the user may be granted read access to the full filesystem 242 for purposes of selecting a file or folder, but the user isnot granted write access to file system 242. Therefore, the user isprevented from modifying file system 242 maintained by LVM 240 in anyway.

In step 440, after the user selects a file or folder, a copy of theselected file or folder is created. The copy of the selected file orfolder is then inserted into the restricted file system associated withthe UCVM. As a result of inserting the copy of the selected file orfolder in the restricted file system associated with the UCVM, anapplication executing in the UCVM may have read and write access to thecopy of the selected file or folder in the virtual file system, but isprevented from effecting any change to the original copy of the selectedfile or folder in file system 242 maintained by LVM 240.

The steps of FIG. 4 ensure that files in file system 242 maintained byLVM 240 are not visible to a UCVM without explicit permission from theuser. Malicious code running in a UCVM, for example, cannotprogrammatically access files in file system 242 in LVM 240. Further,malicious code running in a UCVM also cannot render a false userinterface to trick the user into unintentionally providing any userfiles to the malicious code, since all code responsible for renderingthe user interface is maintained within VMO 230, and thus, unreachableand un-hackable by the malicious code.

File System Switch 310 may be implemented in a variety of ways. Forexample, in one embodiment, File System Switch 310 may be implemented bya network file system protocol (NFS or CIFS may be used). A special VM(or LVM 240) may be used as the OS serving the “User Files” shared filesystem. Other VMs “mount” this shared file system using NFS or CIFS (oranother network file system) from the hosting VM. Application softwarein the hosting VM may decide what files are exposed to which VM based oninstructions provided by VMO 230.

In another embodiment, File System Switch 310 may be implemented, inpart, by a proprietary protocol for handling communications between thedifferent UCVMs and File System Switch 310. File System Switch 310, insuch an embodiment, may be implemented as part of a special VM or in LVM240.

Cloning A UCVM from a Template

In an embodiment of the invention, every virtual machine created inclient 220 is instantiated using a template selected from one or moretemplates 238 stored in VMO 230. In an embodiment, each template in oneor more templates is either immutable or may be updated in a verycontrolled fashion.

Each of one or more templates 238 may be used to instantiate or create avirtual machine with different characteristics or operationalparameters. The characteristics or operational parameters described by atemplate may be configured, tailored, or suited for a particular contextor type of processing activity. For example, each template may specifywhat type of code is to be run within a virtual machine created usingthe template, a size of the virtual machine created using the template,firewall settings for the virtual machine created using the template,what type of virtual machine (for example, a VVM, UCVM, or a LVM) is thebe created using the template, how changes to a local file system withinthe virtual machine created using the template are to be persisted, andwhat portion, if any, of the network can a virtual machine created usingthe template access.

One or more devices internal to client 200 or externally connected toclient 200 may interact with one or more processes executing in avirtual machine within client 200. In an embodiment, a template mayassign responsibility for a selected set of devices to a virtual machinecreated using the template. In other embodiments, responsibility for aselected set of devices may be assigned to a particular virtual machineby virtue of policy data stored on client 200. Such policy data maydescribe one or more policies provided to client 200 from an owner orresponsible organization of client 200. Policy data of this nature maybe maintained by VMO 230 or LVM 240, for example, in certainembodiments.

In an embodiment, one or more templates 238 may be arranged in ahierarchy such that there is a root node corresponding to a templatehaving a default set of characteristics. The root node may have one ormore child nodes, and each of these child nodes may be associated with atemplate that inherits the properties of the parent template, butcontains additional or changes properties associated with that childnode. Naturally, each child node may also have children, and so thehierarchy of templates may be an arbitrary number of levels deep, whereeach template inheriting characteristics of its parent, but yet eachtemplate is capable of further defining or changing characteristics thatdistinguishes the template over its parent.

Branches of the hierarchy of templates may be associated with, or moreparticularly suited, different types of activity. For example, certaintemplates may be associated with corporate activity, and may thereforespecify characteristics related to virtual machines running corporateapplications. Similarly, certain templates may be associated with theuser's personal application's activity or Internet/Web related activity,and may therefore specify characteristics related to virtual machinesrunning the user's own applications or Internet/Web applicationsrespectively.

FIG. 5 is an illustration of instantiating a plurality of differentvirtual machines using different templates according to an embodiment ofthe invention. In FIG. 5, CVM-0 represents a template that defines avirtual machine having characteristics suitable for running a corporateapplication, PVM-0 represents a template that defines a virtual machinehaving characteristics suitable for running a user application(non-corporate), and WVM-0 represents a template that defines a virtualmachine having characteristics suitable for running an Internetapplication. Other embodiments of the invention may define a variety ofother templates to define different types of templates. In the exampleof FIG. 5, cognitive assist module 236 in VMO 230 may use CVM-0 toinstantiate one or more corporate virtual machines, such as CVM-1,CVM-2, etc. Similarly, cognitive assist module 236 may use PVM-0 toinstantiate one or more personal (non-corporate) virtual machines, suchas PVM-1, PVM-2, etc., and cognitive assist module 236 may use WVM-0 toinstantiate one or more web-based virtual machines, such as WVM-1,WVM-2, etc. As depicted in FIG. 5, each instantiated UCVM connects to anexternal network through Firewall VM 250. Cognitive assist module 236can either create these templates on demand or create and store themwhile monitoring the usage of the client.

Installation of Software

In the normal operation of a typical PC, a fair amount of after-marketsoftware is installed. Such after-market software installed on a PCgenerally falls into one of two categories, namely (a) validatedsoftware (packages or straight executables) installed by the ITadministrator of the PC or (b) end-user installed software (includingweb browser plugins & extensions, more complex software packages that gothrough an explicit install phase, and straight executables that can beexecuted without an explicit installation phase). Note that end-userinstalled software may be signed (by a verifiable, known vendor) orunsigned.

In embodiments of the invention, installation of validated software isperformed as is normally performed today. The IT administrator canmanage corporate validated software using embodiments using similarprocedures as performed today, except that such corporate validatedsoftware are installed in LVM 240 (or if need be, VVM 266).

With respect to end-user installed software, IT administrators have twochoices for how they would like to handle this type of installationusing embodiments of the invention. The first choice is for the ITadministrator to lock down client 200 by disallowing any installation ofend-user installed software. While this is a safer operating decision,this approach may reduce the end-user's productivity because the enduser cannot take advantage of applications that may be otherwise usefulthat have not yet been validated by the IT administrator. The ITadministrator may provide installation support on an individual andas-needed basis whenever a user wishes to install any end-user installedsoftware; however, doing so will increase the cost of support by the ITadministrator.

The second choice is for the IT administrator to allow the user toinstall end-user installed software him or herself using featuresprovided by embodiments of the invention. End-user installed softwaremay include browser plugins, browser extensions, signed and unsignedinstallation packages, and straight executables. Browser plugins areinstalled into an installed browser plugin database that is maintainedin a particular UCVM. The installed browser plugin database may beimplemented, in an embodiment, using file and registry diff store 820shown in FIG. 8, which is an illustration of safely installing anuntrusted application according to an embodiment of the invention of theinvention. During installation of a plugin, the installed browser plugindatabase is also updated to record the domain that was used to initiatethe plugin install. Presumably, this is the web page that contains anelement or component that requires the plugin to render the completecontent in the web page. Subsequently, the web browser loads aninstalled plugin into a web HTML/JS engine instance (which runs inside aUCVM) only if the domain of the web page to be displayed by the UCVMmatches a domain, recorded in the plugin database, associated with theinstalled plugin. A plugin that is used by multiple sites is installedonly once, but is associated with multiple domains. Popular plugins likeFlash may be pre-installed in certain embodiments.

Browser extensions may be installed into a web browser's extensiondatabase that is maintained in a particular UCVM. During runtime,browser extensions are treated like web applications in that eachbrowser extension is run inside its own UCVM. In an embodiment, the webbrowser extension database and the installed browser plugin database maybe implemented in the same database in a single UCVM.

Signed installation packages may be run and the resulting installationmay update either the LVM image or the Generic Windows image based on apolicy set by the IT administrator.

Unsigned installation packages go through a virtual install. The virtualinstallation of unsigned installation packages will be described withreference to FIG. 8, which is an illustration of safely installing anuntrusted application according to an embodiment of the invention of theinvention. A registry and program files change set is created and storedin file and registry diff store 820. Start-menu and desktop changes bythe installer are captured in a special folder which contains desktopand start menu items for all user-installed applications. Subsequently,if an unsigned application is run, it is run in a UCVM cloned from theGeneric Windows image all by itself. Virtual disk 810 in FIG. 8 is thenormal virtual disk of the UCVM. DiffStore 820, which furthervirtualizes the file system and the registry as seen by the applicationsof UCVM, is typically implemented as a separate module outside of thenormal block level virtual disk store.

Signed and unsigned executables may be run in a UCVM. Such a UCVM may becreated on demand and destroyed after its use is ended by embodiments.

Managing Web Cookies and Caches

A web cookie (or simply “cookie”) is a piece of text stored on a user'scomputer by their web browser. A cookie can be used for authentication,storing web site preferences, shopping cart contents, the identifier fora server-based session, or anything else that can be accomplishedthrough storing text data.

While the actual cookie itself is not visible to the user, the userwould notice a difference in the user experience of interacting with aweb site if cookies could not be saved between visits to the web site.Accordingly, embodiments of the invention provide mechanism to storecookies before a UCVM is destroyed, so that the next time the uservisits the web site using a web browser running in a different UCVM, anycookies that have been stored and are associated with that web site maybe injected into the new UCVM.

Similarly, to provide the best user experience, it would be advantageousto carry over the cache of a web browser for a particular web domainfrom one UCVM to the next, so that the next time the user visits the webdomain using a different UCVM, there is no a delay in displaying contentdue to an unpopulated cache. Thus, embodiments of the invention providemechanism to store the web cache of a web browser for a web domainbefore a UCVM is destroyed, so that the next time the user visits theweb site using a web browser running in a different UCVM, the cache ofthe web browser need not be warmed (i.e., repopulated), as the cache inthe new UCVM has been updated to contain all the objects the cachepreviously contained in the prior, and now destroyed, UCVM used to visitthe web domain.

To provide a concrete example with reference to the example of FIG. 2,assume that a user initially transparently uses UCVM 260 to run a webbrowser to visit web site A. When UCVM 260 is destroyed, any cookies andcache files are extracted and saved. Thereafter, assume the usertransparently uses UCVM 262 to run a web browser to visit web site B. Asweb site B is hosted by a different web domain than web site A, thepreviously stored cookies and cache files associated with web site Awill not injected into UCVM 262. Thereafter, if UCVM 262 is destroyed,then any cookies and cache files are extracted and saved. At a laterpoint in time, if the user thereafter transparently uses UCVM 264 to runa web browser to visit web site A, then the previously stored cookiesand cache files associated with the web domain of web site A will beinjected into UCVM 264. This allows the web browser running in UCVM 264to visit web site A to appear, to the user, to have the same state ofthe prior web browser used to visit web site A, even through differentvirtual machines are used between visits. Note that no portions of thefile system are saved between visits to a web site; only the state ofthe web session is saved.

In one embodiment, the cookies and cache information is captured in DiffStore 820 associated with the URL of the website. In each visit to thesame URL, the UCVM utilizes the same Diff Store presenting the cookiesand caches to the UCVM. In another embodiment, the cookies and cachefiles can be captured at the end of the session and saved to the clientsystem's core file system in a special folder. On visiting the same URLagain, the cookies and cache can be re-injected into the file system ofthe UCVM.

Efficient Physical-to-Virtual Disk Conversion

Platform virtualization is performed on a given hardware platform byhost software (a control program), which creates a simulated computerenvironment, a virtual machine, for its guest software. A hypervisor,also called virtual machine manager (VMM), is one of many hardwarevirtualization techniques that allow multiple operating systems, termedguests, to run concurrently on a host computer. The hypervisor presentsto the guest operating systems a virtual operating platform and managesthe execution of the guest operating systems. A guest OS executes as ifit was running directly on the physical hardware. Access to physicalsystem resources such as the network access, display, keyboard, and diskstorage is suitably virtualized so that guest OS does not know these arevirtual devices.

Generally, there are two types of hypervisors. Type 1 (or native, baremetal) hypervisors run directly on the host's hardware to control thehardware and to manage guest operating systems. A guest operating systemthus runs on another level above the hypervisor. Type 2 (or hosted)hypervisors run within a conventional operating system environment. Withthe hypervisor layer as a distinct second software level, guestoperating systems run at the third level above the hardware. In otherwords, Type 1 hypervisor runs directly on the hardware; a Type 2hypervisor runs on another operating system, such as Windows.Embodiments of the invention may use any type of hypervisor. Thus,hypervisor 220 in FIG. 2 may either be a Type 1 or a Type 2 hypervisor.

A virtual disk image is a file on a physical disk, which has awell-defined (published or proprietary) format and is interpreted by ahypervisor as a hard disk. In terms of naming, a virtual disk image mayhave a specific file type extension, e.g., .vmdk for VMware VMDK, .vhdfor Xen and Microsoft Hyper-V, and .vdi for Oracle VM VirtualBox.

There are two approaches employed for storage allocation by priorhypervisors, namely, (1) pre-allocate the entire storage for the virtualdisk upon creation and (2) dynamically grow the storage on demand. Inthe former approach involving pre-allocation, the virtual disk may beimplemented as either split over a collection of flat files (typicallyone is 2 GB in size) or as a single, large monolithic flat file. In thelatter approach involving on-demand growth, the virtual disk may also beimplemented using split or monolithic files, except that storage isallocated on demand.

There are two modes in which a disk can be mapped for use by a virtualmachine. In a virtual mode, the mapped disk is presented as if it is alogical volume, or a virtual disk file, to the guest operating systemand its real hardware characteristics are hidden. In a physical mode,also called the pass through mode, the hypervisor bypasses the I/Ovirtualization layer and passes all I/O commands directly to the disk.

A virtual machine (VM) is a software implementation of a machine (i.e. acomputer) that executes programs like a physical machine. Virtualmachines allow the sharing of the underlying physical machine resourcesbetween different virtual machines, each running its own operatingsystem. The software layer providing the virtualization is called ahypervisor, such as hypervisor 220 in FIG. 2.

Virtual machines each require their own image of the operating system.The guest OS and host OS typically do not share the OS image, even ifthey are the same OS. This is problematic for several reasons. First, ifa user wishes to run 10 different virtual machines, then she willrequire 10 different copies of the OS for the guest OSs, which requiresan undesirable amount of storage to maintain. As she is already runningone virtual machine at the host, the total number of different copies ofthe OS required would be 11. Second, the OS for a VM has to be createdeither by installing a new OS or shipping a copy of the OS fromsomewhere else, which is burdensome for those who do not have access toOS images. Further, it is also time consuming to install a new OS orship an OS image, which is typically quite large. A third problem isthat any software present in the host OS (such as a printer driver) willnot be available in a guest OS unless it is installed again.

Shadow Copy (Volume Snapshot Service or Volume Shadow Copy Service orVSS) is a technology included in Microsoft Windows that allows takingmanual or automatic backup copies or snapshots of data (termed “shadowcopies”), even if it has a lock, on a specific volume at a specificpoint in time over regular intervals. VSS operates at the block level ofthe file system. Shadow Copy is implemented as a Windows service calledthe Volume Shadow Copy service. Software VSS provider service is alsoincluded as part of the Microsoft Windows OS to be used by Windowsapplications. Shadow Copy technology requires that the file system to beNTFS to be able to create and store shadow copies. Shadow Copies can becreated on local and external (removable or network) volumes by anyWindows component that uses this technology, such as when creating ascheduled Windows Backup or automatic System Restore point.

Snapshots have two primary purposes. First, they allow the creation ofconsistent backups of a volume, ensuring that the contents cannot changewhile the backup is being made. Second, they avoid problems with filelocking. By creating a read-only copy of the volume, backup programs areable to access every file without interfering with other programswriting to those same files. Through the integration between the VolumeShadow Copy Service, hardware or software VSS providers, applicationlevel writers and backup applications, VSS enables integral backups thatare point in time and application level consistent without the backuptool having knowledge about the internals of each application. The endresult is similar to a versioning file system, allowing any file to beretrieved as it existed at the time any of the snapshots was made.Unlike a true versioning file system, however, users cannot trigger thecreation of new versions of an individual file, only the entire volume.

Embodiments of the invention overcome this limitation by creatingvirtual disks based on VSS shadow copies. FIG. 6 is an illustration of avirtual disk based on VSS shadow copies according to an embodiment. Thevirtual disk of FIG. 6 allows for many guest OSs running on the samehost to share the same OS copy with the host OS. VSS shadow copies maybe created fast and efficiently. Creating virtual disks on top of VSS isalso a very fast operation, which means that VMs (with same OS as hostOS) can be created very efficiently. Shadow copies are also maintainedcheaply by windows OS by keeping the changes since the time shadow wascreated. Hence, the disk usage of multiple VMs is reduced substantially.VMs can also be maintained very efficiently since VSS snapshots can beupdated once and have the changes reflected in all VMs. Since a VSSshadow copy contains all the software the user has installed on themachine at the time of the VSS shadow copy creation, virtual disks alsoreceive access to all the software. Moreover, the version of thesoftware, including any patches installed, is exactly the same. Inaddition to all the software, user documents are also visible to virtualmachines. A virtual disk of an embodiment is an accurate point-in-timecopy of host physical disk.

In an embodiment where VSS snapshots are read-only, a ‘Delta Store Disk’may be attached to the virtual disk. The Delta Store disk is used tocapture all the changes being made to the virtual disk.

Security Afforded by Embodiments

Embodiments of the invention provide a secure environment to preventmalicious code from affecting any lasting change in a computer system.Arbitrary code (either a web application or a native executable) runsinside an isolated operating system running on an isolated virtualmachine. This code has no access to any other application (either anative application or a web application) being run by the user becausethose applications run in other operating systems running in separatevirtual machines. Moreover, arbitrary code has access to only thespecific part of the file system that is needed for correct execution ofthe code. Access to additional parts of the file system has to beprovided by code that runs in VMO (which is secure and fortified againstunauthorized intrusion) and any increased access needs explicitauthorization from the human user.

Specific trusted code that needs to interact in a complex way with otherapplications may be explicitly designated to run together inside thesame designated VM. This type of VM also has limited access to the filesystem.

All code has limited network access to just what that code needs for itscorrect execution. All virtual machines are created from templatesstored in VMO which are either immutable or can be updated in a verycontrolled fashion. Consequently, if a security bug exists in a piece ofcode, the effect of the security bug is isolated (“space limited”)because the compromised code has access to only a limited part of thefile system, the network, devices, etc. Moreover, the effect of thesecurity bug is “time limited” because the virtual machine that has beencompromised will be subsequently discarded and a new virtual machine iscreated for future application instances from a clean immutable VMtemplate.

Using Policy Data to Manage the Deployment of Virtual Machines

Embodiments allow code that originates from arbitrary external sourcesto be safely executed by a client. In this way, digital content ofunknown trustworthiness may be safely received and potentially executedand/or interpreted by a client without incurring the risk that thedigital content contains malicious code that could cause undesirableconsequences.

The ‘digital content’ received by the client from an external source maycorrespond to any type of digital data, such as executable code ornon-executable, interpreted data for example. Since malicious code maybe carried within certain types of non-executable data and subsequentlyspread when the data is interpreted by applications, embodiments treatall incoming digital content as being capable of containing maliciouscode, even if the digital content is not in a recognized executableform. Non-limiting, illustrative examples of digital content include an“.exe” file, an application, a collection of applications designed torun together, a portion of an application, an email attachment, a slidepresentation, a text document, and a web page (which essentially is aportion of an application, namely a web browser). Even though the emailattachment, the slide presentation, and the text document, in and ofthemselves, are not executable files, embodiments of the invention treatthese forms of digital content as potentially carrying malicious code.

To manage the risk posed by receiving digital content of unknowntrustworthiness, any digital content received by a client is stored inone or more virtual machines. In an embodiment, digital content receivedfrom an external source may immediately be stored in one or more virtualmachines upon receipt. Alternately, digital content received from anexternal source may be stored in an intermediate location, such as alocal cache, prior to storing the digital content in a virtual machine.

While embodiments are configured to process all digital contentoriginating from an external source in a virtual machine, the complexityof determining in which virtual machine the digital content should bestored and how that virtual machine should be configured is hidden fromthe user whenever possible or appropriate. To accomplish this goal,techniques are discussed herein for programmatically managing aplurality of virtual machines on the client to accommodate the widevariety of use cases for receiving digital content at a client. However,in some cases, explained in more detail below, it may be appropriate toinform the user of certain activity concerning a virtual machine, suchas when obtaining express permission from the user is advisable beforeperforming an action.

Certain sources of digital content are more trustworthy than othersources. For example, the web site of a bank or Fortune 500 company maybe more trustworthy than the web site of a smaller company or lessorknown organization. Also, applications may have different operatingneeds, e.g., certain applications may be designed to work closely withother applications or require access to network resources. Thus, in anembodiment, the attributes of each virtual machine are specificallytailored to reflect the type of digital content and/or applicationsoperating or stored therein.

To illustrate how one embodiment operates, when a client determines thatdigital content , originating from an external source, is to be receivedor processed by the client, the client may identify, without humanintervention, one or more virtual machines, executing or to be executedon the client, into which the digital content is to be received. To doso, the client may consult policy data, such as policy data 239 storedat client 200 of FIG. 2, to determine a placement policy, a containmentpolicy, and a persistence policy used in identifying the one or morevirtual machines into which the digital content is to be received.

The policy data may be used to specifically tailor the operation of eachvirtual machine to reflect the type of digital content and/orapplications operating or stored therein. The placement policyidentifies a particular virtual machine into which the digital contentis to be stored, the containment policy identifies what networkresources and client resources the particular virtual machine canaccess, and the persistence policy identifies whether data (or a part ofit) stored in the particular virtual machine is persistently stored.Naturally, the placement policy, containment policy, and persistencepolicy are, to a certain extent, intertwined, as the resources a virtualmachine may access and whether data stored therein is persisted willaffect what applications/digital content are appropriate to residetherein.

In an embodiment, each of the placement policy, the containment policy,and the persistence policy may consider a variety of different factors.For example, the placement policy, the containment policy, and/or thepersistence policy may consider a historical record of use for theclient in identifying a virtual machine. The evaluation of a policy mayinvolve consulting a historical record of how the client, orapplications running thereon, has been used. In this way, if aparticular action has been judged to be more safe (or less safe) over aperiod of time, the manner in which the action is handled by the policymay evolve over time. To illustrate, in an embodiment, if a particularnetwork resource, such as an affiliate corporate web page, isdemonstrated to be sufficiently safe over a period of time, then thisweb page may be processed using relaxed restrictions, e.g., by a webbrowser in a virtual machine already handling another trusted web pageas opposed to instantiating a new virtual machine to handle theaffiliate corporate web page. On the other hand, if the historicalrecord of use demonstrates that an action involving a particular networkresource or client resource may pose some risk to the client, then thepolicy may subsequently handle this action more sensitively than before,e.g., by assigning code to handle the particular network resource orclient resource in a dedicated virtual machine with restricted access toclient and network resources.

As another example of the types of factors which may be considered by apolicy, one or more of the placement policy, the containment policy, andthe persistence policy may consider a current physical location of theclient or to which networks the client currently has access inidentifying one or more virtual machines which should be used to receivecontent. In this way, which networks are available to the client, the IPaddress assigned to the client, the current location of the client basedon global positioning service (GPS) data, and the current location ofthe client based on an IP address or which networks are available to theclient may all be considered when determining which virtual machineshould receive digital content and what restrictions should be placed onthat virtual machine. In this way, when the client is physically locatedin an area deemed safe (such as a work office or home), digital contentreceived by the client may be handled by a virtual machine having a setof lesser restrictions than when the client is physically located in anunknown area.

As another example of the types of factors which may be considered by apolicy, one or more of the placement policy, the containment policy, andthe persistence policy may consider the proximity of the client to awireless device, such as a Bluetooth enabled cell phone. For example, ifthe client is not within a configurable distance to the cell phone ofthe user of the client, then the client may receive digital contentusing a set of greater restrictions, e.g., code executing in all virtualmachines may be denied access to certain client resources and/or allnetwork resources. Embodiments may determine whether the client iswithin a configurable distance to a wireless device using a variety ofdifferent methods, such as accessing the wireless signal strengthbetween the client and the wireless device.

In an embodiment, at least a portion of the policy data, used inidentifying one or more responsible virtual machines to receive digitalcontent, is obtained from a remote server after the client determinesthat digital content is to be received from an external source. In thisway, policy data may be sent, as needed, from an IT administrator to theclient. The client may treat any policy data already residing on theclient in the same manner as policy data retrieved from a remote server.For example, when a user of the client performs an action, the clientmay consult a remote server to see if the remote server has anyadditional policy data regarding this action. Following this procedure,an IT administrator can maintain a high level of control on how theclient will manage virtual machines running on the client. This enablesthe IT administrator to make adjustments to the security model followedby the client in real-time. The client may interact with a humanoperator at a remote location to obtain additional policy data or mayinteract with a remote automated system, without human intervention, toobtain the additional policy data. Note that certain embodiments may beconfigured to consult a remote server for policy data only when acertain configurable action is taken. Therefore, in certain embodiments,the client need not always contact a remote server to determine ifadditional policy data is available each time that the client is toreceive new digital content.

In an embodiment, the policy data may specify that the virtual machineassigned to receive digital content can only access a limited subset ofthe metadata properties for a client resource or a network resource. Forexample, a virtual machine may not be capable of determining what localwireless networks are available in the vicinity or whether the networkcard of the client is of a particular type. In this way, the amount andtype of information exposed to a particular virtual machine may becontrolled to a fine level of granularity.

Use of the placement policy, the containment policy, and the persistencepolicy by certain embodiments will be discussed in further detail below.

Placement Policy

The placement policy identifies a particular virtual machine into whichthe digital content is to be stored. The particular virtual machineidentified by a placement policy in which digital content is to bestored may be an existing virtual machine or a new virtual machine thathas not yet been instantiated. In the case where the placement policyspecifies that the digital content should be received by a virtualmachine that has not yet been instantiated, either the placement policyitself or some other location in the policy data will identify atemplate for use in instantiating the particular virtual machine. Theidentified template will describe characteristics of a virtual machinesuitable for receiving the digital content.

The placement policy may weigh a variety of different considerations indetermining which virtual machine should store the digital content sothat the digital content may be safely executed, interpreted, and/orprocessed. For example, a placement policy of an embodiment may assignany file having a certain name or certain attributes to a virtualmachine having certain characteristics. To illustrate, a placementpolicy may indicate that all signed executable files from an internalorganization or company are to be assigned to a virtual machine having aspecified set of characteristics. As another example, the placementpolicy may instruct untrusted applications to execute in separatevirtual machines so that each untrusted application is isolated fromother applications and data of the client.

The placement policy of an embodiment may identifies a plurality ofclasses of virtual machines, where each class of the plurality ofclasses is associated with a different trust level for external sourcesof digital content. Code executing in a virtual machine cannot accessexternal sources associated with less trustworthy external sources ofdigital content. For example, assume there are three classes of virtualmachines, where the first class of virtual machines is designed to runweb browsers accessing web sites of financial institutions and emailproviders, the second class of virtual machines is designed to run webbrowsers accessing web sites of Fortune 500 companies, and the thirdclass of virtual machines is designed to run web browsers accessing allother web sites. In this example, a web browser executing in a virtualmachine that is associated with the third class cannot access any websites from Fortune 500 companies or financial institutions and emailproviders. Similarly, in this example, a web browser executing in avirtual machine that is associated with the second class cannot accessany web sites from financial institutions and email providers.

The placement policy of an embodiment may identify the particularvirtual machine into which the digital content is to be received byobserving application dependencies. Such a policy recognizes that insome instances, it is helpful or even necessary to execute certainapplications within a single virtual machine. For example, certainproviders of software applications may design their softwareapplications do work together or integrate with each other to a highdegree. In this case, it would be advantageous to have applications thatare designed to work together to run within a single virtual machine.One way for the placement policy to make this determination would be toask the user whether an application being installed is dependent uponanother application already installed at the client to ensure that bothapplications may be run in the same virtual machine. While this doesexpose the notion of a virtual machine to the user, a user need onlymake a decision of this nature when an application is installed on theclient, and thus, this decision may be made by IT administrators orother knowledgeable personal rather than relying upon the end user ofthe client to make such a decision.

Alternatively, determining whether an application being installed isdependent upon another application may be made programmatically byexamining the dependencies during the installation of that application.For example, during the installation of application A, the installprocess may check if module B is already installed or may require thatmodule B already by installed. In this example, the placement policy maydetermine then that application A has a dependency with module B and maytherefore allow application A to run in same virtual machine as moduleB.

To illustrate another example, it is initially noted that there need notbe a one to one correspondence between a web browser and a web page. Forexample, a web browser may comprise many tabs, and each tab may displaya different web page. In addition, each web browser may have a varietyof different plug-in and/or associated programs which may be treated asor considered a separate application. Since a web browser may displaymultiple web pages of varying trust levels, it is desirable toaccommodate a web browser having multiple tabs without requiring thatthe web pages displayed by each tab reside in the same virtual machine.For example, if a web page contains malicious code, then it would bebeneficial to execute it in a different virtual machine from the virtualmachine containing the web page of your bank. Therefore, in anembodiment, the placement policy may specify that web page of certainsources should be received in a separate virtual machine. While the usermay see a single web browser having two tabs, on the back end this maybe implemented in two separate virtual machines that each execute a copyof the web browser and possess one web page to be shown in associatedwith one tab of the web browser. A practical implementation of web pageplacement may use a VM per web-site placement policy.

These are merely examples of how a placement policy may be implemented.It is contemplated that actual implementations of a placement policywill be configured based upon the particular needs and concerns of theend user. The containment policy of certain embodiments will now bepresented in greater detail.

Containment Policy

The containment policy identifies what network resources and clientresources a particular virtual machine can access. Network resources, asbroadly used herein, refers to any resource that is external to theclient while client resources, as broadly used herein, refers to anyresources that is internal to the client. A client resource may includeany device, component, and/or data residing on or accessible to theclient, such as a digital camera, a network interface card, a digitalclock, the current time, files, pictures, and email.

The containment policy is used to ensure that code running within avirtual machine has access to only those resources deemed necessary fornormal and intended operation. For example, email attachments should notneed access to the Internet (generally speaking), and so they should beopened in a virtual machine that is configured such that it does nothave access to the Internet.

In an embodiment, the containment policy may specify what portion of thenetwork that is available or exposed to code executing within a virtualmachine. For example, the containment policy may specify that codeexecuting within a particular virtual machine may access no networkresources, all network resources, or a subset of the network resources.Thus, a containment policy may specify that code executing within avirtual machine may access a first set of network resources and may notaccess a second set of network resources. Embodiments may specify whatparticular network resources are available to a virtual machine usingany level of granularity, e.g., only certain types of network resourcesmay be exposed, only certain properties of network resources may beexposed, or only certain portions of the network may be exposed.

In an embodiment, enterprise applications may be grouped intocollections. Groupings may be based on a variety of factors, such as jobfunctions or business unit, for example. Each grouping of applicationsmay be executed within a single virtual machine according to anembodiment.

To illustrate the interaction between the containment policy and clientresources, the containment policy of an embodiment identifies eachclient resource accessible to a virtual machine. For example, acontainment policy may specify whether code executing in the particularvirtual machine can perform one or more of the following actions: accessa USB port on the client, perform a copy operation or a paste operation,access a network to which the client is connected, access a GPS deviceof the client, location information for the client, or tilt informationfor the client, access a printer or facsimile machine to which theclient is connected, and access a digital camera or screen data for theclient. Note that these exemplary actions are not meant to provide anexhaustive list, as a containment policy may be used to specify, withparticular specificity, which client and network resources may beaccessed by code executing within a virtual machine. In this way, if anew client resource becomes available, such as fingerprint scanningdevice, the containment policy may be updated to reflect the new clientresource available to the client.

In an embodiment involving the receipt of executable code at a client,the containment policy may specify that the executable code is deniedaccess to a user file without first obtaining a user's permission toallow the executable code to access the user file. In this way, virtualmachines may be configured to allows request permission each timeexecutable code therein access a user file, thereby allowing the user tobe informed of the intentions of the executing code and presumablyprevent unauthorized access to the user's own files. Such a permissionscheme might be implemented naturally as part of the normal user workflow of picking a file to open by running the permission code in a cleanprotected VM separate from the VM running the untrusted code which ismaking the request.

To illustrate the interaction between the containment policy and networkresources, the containment policy of an embodiment identifies whethercode executing in a particular virtual machine can one or more networksaccessible to the client. As another example, the containment policy ofan embodiment identifies which, if any, objects stored over a networkthe virtual machine can access. For example, a virtual machine may berestricted to access a specified set of objects or files on a particularserver or a particular set of web pages.

In an embodiment, the containment policy may consider any number offactors, including but not limited an identity of the user of theclient, a set of properties of the digital content, a physical locationof the client, the current time, a holiday schedule, and a set ofadministrator-specified policy rules. In this way, the containmentpolicy may assign a virtual machine having more restrictions than usualto receive digital content when the digital content is deemed morelikely to contain malicious code. For example, it may be deemed likelythat digital content contains malicious code when it is received by theclient outside of normal business hours, over a holiday, at a time whenthe client is outside of the user's home or work office, or when thedigital content has certain suspicious properties. In this way, thecontainment policy may assign suspicious digital content to be receivedin a virtual machine having additional restrictions appropriate for suchsuspicious digital content.

These examples of how a containment policy may operate and merelyillustrative of some examples and are not intended to be an exhaustivelist, as actual implementations of a containment policy will beconfigured based upon the particular needs and concerns of the end user.The persistence policy of certain embodiments will now be presented ingreater detail.

In an embodiment, the persistence policy identifies whether data storedin a particular virtual machine is persistently stored. The policygrapples with the issue of whether or not to save state created byuntrusted code and if so, whether the state should be stored in anisolated manner or merged back into the main file system of thecomputer. On one hand, to provide a convenient user experience, it maybe helpful to persistently store cookies for a web site. On the otherhand, it would not be desirable to persistent malicious code, such as akey logger, that was inadvertently introduced into a virtual machine bymalware downloaded into and run in the affected virtual machine.

The persistence policy, hand in hand with the placement policy, shouldbe designed to ensure that any potentially malicious code is notpersistently stored, or in the alternative, persistently stored in anisolated way. This way, if malicious code, such as a key logger, ispersistently stored, and in any future invocation (execution orinterpretation), it is invoked (executed) in the context of a possiblynew virtual machine instance separate from any other code, therebynullifying the risk presented thereby.

To illustrate an illustrative persistence policy, in an embodiment onlycookies and cache files are persistently stored in a virtual machine inwhich a web browser executes. Further, the cookies and cache filesassociated with a particular web site are only inserted to a virtualmachine that is intended to execute a web browser displaying that website. Thus, cookies and a cache file associated with site A would not beinserted into a virtual machine instantiated to run a web browser todisplay web site B, but would be inserted into a virtual machineinstantiated to run a web browser to display web site A.

The above discussion of a persistence policy is exemplary of certainembodiments and is not intended to describe all implementations of apersistence policy, as a persistence policy will be configured basedupon the particular needs and concerns of the end user.

Unified Display

Even though there may be a plurality of virtual machines executing atthe client, this complexity need not be exposed to the end user of theclient. Thus, the end user should be presented visual content generatedfrom each virtual machine executing on the client in a unified manner topresent a single, cohesive presentation to the end user of the client.The presentation of the content should be seamless and close to nativeas possible.

For example, the end user of the client should interact with a webbrowser that looks like a known web browser, even though the webbrowser, at the back end, is implemented using a plurality of virtualmachines to execute copies of the web browser and different web pagescorresponding to each tab of the web browser.

Hardware Mechanisms

In an embodiment, client 200 of FIG. 2 may be implemented on, include,or correspond to a computer system. FIG. 9 is a block diagram thatillustrates a computer system 900 upon which an embodiment of theinvention may be implemented. In an embodiment, computer system 900includes processor 904, main memory 906, ROM 908, storage device 910,and communication interface 918. Computer system 900 includes at leastone processor 904 for processing information. Computer system 900 alsoincludes a main memory 906, such as a random access memory (RAM) orother dynamic storage device, for storing information and instructionsto be executed by processor 904. Main memory 906 also may be used forstoring temporary variables or other intermediate information duringexecution of instructions to be executed by processor 904. Computersystem 900 further includes a read only memory (ROM) 908 or other staticstorage device for storing static information and instructions forprocessor 904. A storage device 910, such as a magnetic disk or opticaldisk, is provided for storing information and instructions.

Computer system 900 may be coupled to a display 912, such as a cathoderay tube (CRT), a LCD monitor, and a television set, for displayinginformation to a user. An input device 914, including alphanumeric andother keys, is coupled to computer system 900 for communicatinginformation and command selections to processor 904. Other non-limiting,illustrative examples of input device 914 include a mouse, a trackball,or cursor direction keys for communicating direction information andcommand selections to processor 904 and for controlling cursor movementon display 912. While only one input device 914 is depicted in FIG. 9,embodiments of the invention may include any number of input devices 914coupled to computer system 900.

Embodiments of the invention are related to the use of computer system900 for implementing the techniques described herein. According to oneembodiment of the invention, those techniques are performed by computersystem 900 in response to processor 904 executing one or more sequencesof one or more instructions contained in main memory 906. Suchinstructions may be read into main memory 906 from anothermachine-readable medium, such as storage device 910. Execution of thesequences of instructions contained in main memory 906 causes processor904 to perform the process steps described herein. In alternativeembodiments, hard-wired circuitry may be used in place of or incombination with software instructions to implement embodiments of theinvention. Thus, embodiments of the invention are not limited to anyspecific combination of hardware circuitry and software.

The term “machine-readable storage medium” as used herein refers to anytangible medium that participates in storing instructions which may beprovided to processor 904 for execution. Such a medium may take manyforms, including but not limited to, non-volatile media and volatilemedia. Non-volatile media includes, for example, optical or magneticdisks, such as storage device 910. Volatile media includes dynamicmemory, such as main memory 906.

Non-limiting, illustrative examples of machine-readable media include,for example, a floppy disk, a flexible disk, hard disk, magnetic tape,or any other magnetic medium, a CD-ROM, any other optical medium, a RAM,a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, orany other medium from which a computer can read.

Various forms of machine readable media may be involved in carrying oneor more sequences of one or more instructions to processor 904 forexecution. For example, the instructions may initially be carried on amagnetic disk of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over anetwork link 920 to computer system 900.

Communication interface 918 provides a two-way data communicationcoupling to a network link 920 that is connected to a local network. Forexample, communication interface 918 may be an integrated servicesdigital network (ISDN) card or a modem to provide a data communicationconnection to a corresponding type of telephone line. As anotherexample, communication interface 918 may be a local area network (LAN)card to provide a data communication connection to a compatible LAN.Wireless links may also be implemented. In any such implementation,communication interface 918 sends and receives electrical,electromagnetic or optical signals that carry digital data streamsrepresenting various types of information.

Network link 920 typically provides data communication through one ormore networks to other data devices. For example, network link 920 mayprovide a connection through a local network to a host computer or todata equipment operated by an Internet Service Provider (ISP).

Computer system 900 can send messages and receive data, includingprogram code, through the network(s), network link 920 and communicationinterface 918. For example, a server might transmit a requested code foran application program through the Internet, a local ISP, a localnetwork, subsequently to communication interface 918. The received codemay be executed by processor 904 as it is received, and/or stored instorage device 910, or other non-volatile storage for later execution.

In the foregoing specification, embodiments of the invention have beendescribed with reference to numerous specific details that may vary fromimplementation to implementation. Thus, the sole and exclusive indicatorof what is the invention, and is intended by the applicants to be theinvention, is the set of claims that issue from this application, in thespecific form in which such claims issue, including any subsequentcorrection. Any definitions expressly set forth herein for termscontained in such claims shall govern the meaning of such terms as usedin the claims. Hence, no limitation, element, property, feature,advantage or attribute that is not expressly recited in a claim shouldlimit the scope of such claim in any way. The specification and drawingsare, accordingly, to be regarded in an illustrative rather than arestrictive sense.

1. A method for transferring data to a client, comprising: in responseto the client determining that digital content, originating from anexternal source, is to be received or processed by the client, theclient identifying, without human intervention, one or more virtualmachines, executing or to be executed on the client, into which thedigital content is to be stored, wherein identifying the one or morevirtual machines comprises the client consulting policy data, stored atthe client, to determine a placement policy, a containment policy, and apersistence policy used in identifying the one or more virtual machines.2. The method of claim 1, wherein the digital content comprisesexecutable code or interpreted code.
 3. The method of claim 1, whereinthe digital content comprises non-executable, interpreted data.
 4. Themethod of claim 1, wherein at least a portion of the policy data, usedin identifying the one or more virtual machines, is obtained from aremote server after the client determines that the digital content is tobe received or processed.
 5. The method of claim 1, wherein one or moreof the placement policy, the containment policy, and the persistencepolicy consider a historical record of use for the client in identifyingthe one or more virtual machines.
 6. The method of claim 1, wherein oneor more of the placement policy, the containment policy, and thepersistence policy consider a current physical location of the client orto which networks the client currently has access in identifying the oneor more virtual machines.
 7. The method of claim 1, wherein the policydata specifies that the one or more virtual machines each can onlyaccess a limited subset of metadata properties of a client resource or anetwork resource.
 8. The method of claim 1, wherein the placement policyidentifies a particular virtual machine into which the digital contentis to be stored, wherein the containment policy identifies what networkresources and client resources the particular virtual machine canaccess, and wherein the persistence policy identifies whether datastored in the particular virtual machine is persistently stored.
 9. Themethod of claim 8, wherein the placement policy identifies theparticular virtual machine into which the digital content is to bestored by observing application dependencies.
 10. The method of claim 8,wherein the placement policy identifies a plurality of classes ofvirtual machines, wherein each class of the plurality of classes isassociated with a different trust level for external sources of digitalcontent, and wherein code executing in the particular virtual machinecannot access external sources associated with less trustworthy externalsources of digital content.
 11. The method of claim 8, wherein theplacement policy specifies that the digital content should be stored bya virtual machine that has not yet been instantiated, and wherein thepolicy data identifies a template for use in instantiating theparticular virtual machine, and wherein the template describescharacteristics of a virtual machine suitable for executable codeoriginating from the external source.
 12. The method of claim 1, whereinthe external source is a web site and the digital content is a web pageto be displayed in a new tab of a web browser executing in a firstvirtual machine on the client, and wherein the placement policyspecifies that the digital content is to be stored by a second virtualmachine separate from the first virtual machine, and wherein the secondvirtual machine should execute a copy of the web browser to display theweb page in the new tab of the web browser.
 13. The method of claim 1,wherein the containment policy considers one or more of the followingfactors: an identity of the user of the client, a set of properties ofthe digital content, a physical location of the client, the currenttime, a holiday schedule, and a set of administrator-specified policyrules.
 14. The method of claim 1, wherein the containment policyspecifies that code executing within the one or more virtual machinesmay access a first set of network resources and may not access a secondset of network resources.
 15. The method of claim 1, wherein thecontainment policy identifies each client resource accessible to each ofthe one or more virtual machines.
 16. The method of claim 1, wherein thecontainment policy identifies whether code executing in the particularvirtual machine can access a USB port on the client or a network towhich the client is connected.
 17. The method of claim 1, wherein thecontainment policy identifies whether code executing in the particularvirtual machine can perform a copy operation or a paste operation. 18.The method of claim 1, wherein the containment policy identifies whethercode executing in the particular virtual machine can access a GPS deviceof the client, location information for the client, or tilt informationfor the client.
 19. The method of claim 1, wherein the containmentpolicy identifies whether code executing in the particular virtualmachine can access a printer or facsimile machine to which the client isconnected or a digital camera or screen data for the client.
 20. Themethod of claim 1, wherein the digital content is an attachment, andwherein the containment policy instructs that a particular virtualmachine, in which the digital content is to be received, should not haveaccess to any network accessible to the client.
 21. The method of claim1, wherein the digital content is executable code, and wherein themethod further comprises: upon the executable code requesting access toa user file, preventing the executable code from accessing the user filewithout obtaining a user's permission to allow the executable code toaccess the user file.
 22. The method of claim 1, further comprising: ata plurality of virtual machines executing at the client, generatingvisual content to be displayed by the client; and presenting the visualcontent generated from each of the plurality of virtual machines in aunified manner to present a single, cohesive presentation to a user ofthe client.
 23. A client, comprising: one or more processors; one ormore storage mediums storing one or more sequences of instructions,which when executed by the one or more processors, causes: in responseto the client determining that digital content, originating from anexternal source, is to be received or processed by the client, theclient identifying, without human intervention, one or more virtualmachines, executing or to be executed on the client, into which thedigital content is to be stored, wherein identifying the one or morevirtual machines comprises the client consulting policy data, stored atthe client, to determine a placement policy, a containment policy, and apersistence policy used in identifying the one or more virtual machines.24. A computer readable storage medium storing one or more sequences ofinstructions, which when executed by one or more processors, causes: inresponse to a client determining that digital content, originating froman external source, is to be received or processed by the client, theclient identifying, without human intervention, one or more virtualmachines, executing or to be executed on the client, into which thedigital content is to be stored, wherein identifying the one or morevirtual machines comprises the client consulting policy data, stored atthe client, to determine a placement policy, a containment policy, and apersistence policy used in identifying the one or more virtual machines.